In a liquid crystal panel, a birefringent film is used so as to control a phase difference of light. There is known, as the birefringent film, those obtained by flow-casting of a coating solution containing an aromatic polymer such as an aromatic polyimide or an aromatic polyester as a main component on a base material such as a glass plate or a polymer film to form a coating film, and orienting the aromatic polymer (Japanese Unexamined Patent Publication No. 2004-70329 A).
A conventional kind of an aromatic polymer has a feature that it is excellent in heat resistance and mechanical strength. On the other hand, the aromatic polymer has a disadvantage that it is inferior in solubility in an organic solvent. Therefore, a birefringent film containing a conventional aromatic polymer as a main component has been formed by dissolving the aromatic polymer in a solvent having high polarity such as cyclopentanone, methyl ethyl ketone or dichloroethane to obtain a solution, followed by flow casting and coating of the solution and further drying. However, since the option of a solution capable of dissolving the aromatic polymer is limited in this film-forming method, drying conditions were limited and expensive facilities were required. Therefore, an aromatic polymer soluble in a solvent having low polarity such as toluene has been required.